1. Field of the Invention
The invention relates to a portable apparatus for testing fetal heart rate using ultrasonic means and also simultaneously detecting a maternal input signal. More particularly, the invention relates to the use of a logarithmic amplification means for amplifying the detected fetal heart signal. The invention also relates to the simultaneous transmission of the fetal and maternal input signals to a remote location using communication linking means.
2. Description of Prior Art
In recent years considerable attention has been directed to enhanced methods for fetal and maternal monitoring techniques and procedures. Fetal monitors are widely used to monitor the fetal heart rate as a means for monitoring the fetal condition. In contrast, maternal uterine contractions have been used both during pregnancy and labor, to yield information about the fetus as well as the advancement of labor. Data on these two factors assist the physician to decide whether the condition of the fetus requires immediate medical attention.
Several conventional fetal monitoring systems are routinely used in the care of patients both prior to and during labor and delivery. Fetal heartbeats are routinely detected from the interior abdominal wall indirectly and directly by one of several means. Several indirect methods involve the use of electrodes which pick up the weak fetal electrocardiogram on the maternal abdomen. A sensitive microphone has also been used which picks up fetal heart sounds, or an ultrasonic Doppler transducer can be employed to detect Doppler frequency shifts in ultrasonic energy reflected from moving components of the fetal cardiovascular system. Stethoscopes have also been used to listen to the fetal heartbeat.
The use of stethoscopes for listening to the fetal heartbeat has been unsatisfactory due to the high degree of extraneous or artifact noise which occurs during periods of labor contractions, and such devices are impractical for in-home patient use. Even prior to the commencement of labor, ordinary stethoscopes have been unsatisfactory for use by a physician because the sound of the fetal heart can be masked by the sound of the mother's heartbeat.
Older ultrasonic Doppler systems for monitoring fetal heart rate have been generally inconvenient to use since it was difficult to find the fetal heart beat, and once found the device had to be repositioned frequently. Most of the ultrasonic Doppler systems available to date include an ultrasound probe together with processing circuitry which is attached by wires to a loudspeaker used by the physician. Other known systems which have utilized Doppler probes are hard-wired to speakers which, for example, can be clipped to the physician's shirt pocket. Such systems, however, do not appear to have been used by a patient for self-testing purposes, let alone used at home with means enabling separate analyses by a physician.
The heart rate of the fetus has also been monitored with various electronic apparatus to determine certain characteristics of the heart beat. This is usually accomplished by using two electrodes one of which is attached to the head of the fetus. Although this technique has provided reasonably accurate data, there are obvious disadvantages. For example, the electrode cannot be attached to the head of the fetus until the cervix has opened sufficiently and the amniotic sack has been ruptured. For obvious reasons, this technique has not been followed to monitor the fetus in the early stages of labor. In addition, the electrode has been applied either blindly or by means of a special light source which requires special training. Furthermore, the presence of a doctor has been required to supervise the electrode attachment, and is totally impractical for in-home use.
In addition to the foregoing difficulties, the frequent movement of the fetus adds to the problem of deriving reliable signals indicative of fetal heart rate. The problem is intensified even more as a consequence of the multiple sounds generated by the heart valves, in addition to the nonsynchronous impulse noise caused by the fetal and mother movements. Naturally, processing of multiple signals with background noise within a single heartbeat, if processed as consecutive heartbeat signals, would produce a false indication of the fetal heart rate, and therefore provide unreliable instrumentation.
One difficulty associated with these monitoring procedures is that they must be performed in a medically controlled environment, namely in a hospital or doctor's office. Many patients, however, prefer not to leave the comfort and security of their home for the sole purpose of having routine testing procedures performed by a skilled medical professional; yet this preference is counterbalanced by the need for such procedures to be carried out. To date, no effective system has been designed which is capable of monitoring both fetal and maternal input signals in a reliable and safe manner at a site remote from these controlled environments. An in-home testing device would not only benefit the patient but also the medical professional.
The patient is benefitted by avoiding the need to visit the hospital (which is currently the only place where such testing is done) which is time consuming and stressful. This is of particular importance in rural areas where the hospital is far away from the patient's home or is difficult to reach during bad weather conditions. The patient is also benefitted by avoiding costly interruption of work habits if the patient can use a monitoring system in the home setting.
Besides the benefits derived by the patient, the prenatal infant also benefits from in-home testing, first and foremost, since patients may avoid taking this test in the stressful environment created by a hospital setting. A less stressful environment also lowers the risks of premature labor, the risk of creating maternal complications, while also enabling the fetal condition to be diagnosed and tracked at its early stage. In addition, outlying hospitals can transmit ongoing labor data to neonatal centers for expert advice to better diagnose the fetal condition, and a doctor can immediately administer the test during an office examination if he suspects a need for such a test.
With regard to the health care organization, such an in-home monitoring system avoids neonatal care for premature babies, where costs can be astronomical. It further enables earlier detection of fetal complications which can avoid unnecessary problems and expenses while saving hospital bed space for patients who require constant monitoring.
Another notable drawback of conventional fetal monitoring systems is that the detecting sensors must be tightly strapped to the patient in order to obtain adequate signals. This obviously is uncomfortable and inconvenient for the patient, and may result in decreased patient compliance with monitoring schedules.
In view of the noted prior art deficiencies, it would be desirable to have a self-contained system that combines (a) data gathering, (b) data storage, (c) data transmission, and (d) display of data to allow for effective prenatal monitoring.